Several long-standing employees lost their jobs in a 2015 restructure just months after they alerted managers to a fake invoice Harrison presented, and questioned her domestic and international travel.

Last week, the ministry's new chief executive, Peter Mersi, announced he had appointed an independent investigator to look into claims staff who were raising red flags about Harrison were restructured out of the organisation.

He had previously declined to investigate the matter.

Two of those who lost their jobs have told RNZ they had no doubt the concerns they raised led to their axing.

State Services Commissioner Peter Hughes said the former employees had now asked him to investigate whether they were unfairly forced out.

"I take their concerns seriously and I am currently considering this request."

Public servants who were worried about an issue needed to raise them so they could be properly considered and addressed, Mr Hughes said.

The Public Service Association has also called for an investigation.

It said the three employees were made redundant only two months after communicating their concerns about Harrison's behaviour.

Its national secretary, Glenn Barclay, said the incident could have a chilling effect on whistleblowing in the public sector and an investigation was needed to uncover the truth.